Add stackedOnTop to make sure the custom element is always rendered on top of all when stackedOnTop is true

src/constants.ts

@@ -159,6 +159,7 @@ export const DEFAULT_CUSTOM_ELEMENT_CONFIG: Required<CustomElementConfig> = {
   svg: "",
   width: 40,
   height: 40,
+  stackedOnTop: false,
 };
 export const MQ_MAX_WIDTH_PORTRAIT = 730;
 export const MQ_MAX_WIDTH_LANDSCAPE = 1000;